We consider three contributions as our most important achievements over the past year. First, we have isolated T cells from the stroma of a transplantable, chemically induced mouse sarcoma by using fluorescence-activated cell sorting, grown these cells in the presence of interleukin 2, and established two lines, one inhibiting the outgrowth of cells from the same sarcoma in Winn assays and the other facilitating this outgrowth. The former cells were primarily Lyt-\1+2+, and thelatter were primarily Lyt 1-2+. Further work in this area should make it possible to define the surface phenotypes and functions of T cells infiltrating growing tumors. Second, we have demonstrated that long-lived small lymphocytes, which are Thy 1+, Lyt 1+2- can localize into growing, transplanted, chemically induced sarcomas and that this localization has a strong tumor antigen specific component. Third, we have demonstrated that the T cell-mediated suppression of tumor immunity has an antigen-nonspecific component, which is triggered by contact between antigen-specific T suppressor cells and the appropriate antigen.